1. Field of the Invention
The present invention relates to an apparatus for generating a set of radio parameters, a transmitter, and a receiver.
2. Description of the Related Art
In the mobile communication systems where video and/or data are mainly communicated, there is need of a much higher capability than in the conventional mobile communication systems (IMT-2000), and a higher capacity, a faster speed, and a broadband connection have to be achieved. In these systems, it is expected that they will be used under various communication environments such as indoor and outdoor areas. Under the outdoor areas, multiple cells (multi-cell) covering a wide area are provided for enabling fast packet transmission for a fast-moving mobile station. Under the indoor areas, because radio waves are attenuated more drastically, access points are provided within buildings without support of radio communications at outdoor base stations. From other viewpoints such as improved utilization efficiency of communication resources, packet-based communications have been employed even in radio segments rather than conventional circuit switched communications. In communications between a mobile station and an apparatus (upper node) located on the upper layer of a base station, particularly in downlink data transmission, not only a unicast scheme but also a multicast scheme and a broadcast scheme are employed. For example, see Non-Patent Reference 1 for an outlook of future communication systems.
On the other hand, frequency selective fading under multipath environments has significant influence in wideband mobile communication systems. Hence, an OFDM (Orthogonal Frequency Division Multiplexing) system is promising as a next generation communication system. In the OFDM system, a single symbol is generated by attaching a guard interval to an effective symbol including information to be transmitted, and multiple symbols are transmitted during a predetermined transmission time interval (TTI). The guard interval consists of part of information within the effective symbol. The guard interval may be also called a cyclic prefix (CP) or overhead.
A receiver receives data on paths with various propagation delays. According to the OFDM system, if the amount of propagation delay falls within the period of the guard interval, inter-symbol interference can be effectively reduced. Thus, a relatively large guard interval allows delay waves to be advantageously combined. This is advantageous particularly in communications with an extremely large cell radius and in simultaneous transmission of the same information from different cells to a mobile station in accordance with the multicast scheme. However, the guard interval includes only part of the effective symbol, and thus a larger period of the guard interval is not preferable from the viewpoint of information transmission efficiency. In some cases, satisfactory communication quality may be maintained under environments with relatively short propagation delay such as urban areas and indoor areas or environments available for the unicast scheme by setting a relatively short guard interval. Therefore, it is impossible to determine a single type of guard interval optimized under various communication environments. For this reason, it may be possible to provide many sets of radio parameters for defining symbols including guard intervals with various sizes to perform radio communications in the adaptively selected optimal symbol format. However, signal processing corresponding to such various symbol formats leads to an extremely heavy workload, which is unfavorable for mobile stations with a relatively simple configuration. For a mobile station having no option of an operating frequency (clock frequency), available signal processing is strictly limited, and thus the aforementioned problem may have a particularly adverse effect on such a mobile station.    [Non-Patent Reference 1] Ohtsu, “Systems beyond IMT-2000”, ITU Journal, Vol. 33, No. 3, pp. 26-30, Mar. 2000